Good morning and thank you for your replies and words of advice.
The colleague is definitely a lesbian. Although I've never met her before, her name has come up over the years and she has dated at least one female work colleague.
I'm very professional when it comes to work, so no one would even know I have this crush and I certainly wouldn't jeopardise either of our work careers. I may need to go back to my old place of work come July, so am conscious time may not be on my side. However, we will both continue to work for the same organisation.
We've had a few awkward moments alone, normally visiting the ladies toilet, where I've been coming out/in and again, we've given each other this very long look and by the time I've come out of the toilet, she's gone!
A couple of her close male work colleagues now have a chat with me, but nothing from her.
No work functions unfortunately and to make matters worse, I'm 'not out' at work.